Not Applicable.
Not Applicable.
Not Applicable.
(1) Field of the Invention
Replacement of the cathode ray tube with a flat panel screen requires a display technology which simultaneously makes it possible to achieve a high image resolution, i.e. more than 1000 lines, a high image brightness ( greater than 200 cd/m2), a high contrast ( greater than 100:1), a high frame rate ( greater than 60 Hz), an adequate color representation ( greater than 16 million colors), a large image format (screen diagonal  greater than 40 cm), a low power consumption and a wide viewing angle, at low production costs. At present, there is no technology which fully satisfies all these features simultaneously.
(2) Description of Related Art
Many manufacturers have developed screens which are based on nematic liquid crystals and have been used in recent years in the field of notebook PCs, personal digital assistants, desktop monitors etc. Use is made here of the technologies STN (supertwisted nematics), AM-TN (active matrixxe2x80x94twisted nematics) AM-IPS (active matrixxe2x80x94in-plane switching) and AM-MVA (active matrixxe2x80x94multidomain vertically aligned), which are described in detail in the literature; see, for example, T. Tsukuda, TFT/LCD: Liquid Crystal Displays Addressed by Thin-Film Transistors, Gordon and Breach, 1996, ISBN 2-919875-01-9, and the references cited therein; SID Symposium 1997, ISSN-0097-966X pages 7 to 10, 15 to 18, 47 to 51, 213 to 216, 383 to 386, 397 to 404 and the references cited therein. Furthermore, use is being made of the technologies PDP (plasma display panel), PALC (plasma addressed liquid crystal), ELD (electroluminescent display), FED (field emission display), which are also explained in the above-cited SID report.
Clark and Lagerwall (U.S. Pat. No. 4,367,924) have been able to show that the use of ferroelectric liquid crystals (FLCs) in very thin cells results in opto-electrical switching or display elements which have response times which are faster by a factor of up to 1000 compared with conventional TN (xe2x80x9ctwisted nematicxe2x80x9d) cells (see, for example, EP-A 0 032 362). Owing to this and other favorable properties, for example the possibility of bistable switching and the fact that the contrast is virtually independent of the viewing angle, FLCs are basically suitable for areas of application such as computer displays and TV sets, as shown by a monitor marketed in Japan by Canon since May 1995.
The use of FLCs in electro-optical or fully optical components requires either compounds which form smectic phases and are themselves optically active, or the induction of ferroelectric smectic phases by doping compounds which, although forming such smectic phases, are not themselves optically active, with optically active compounds. The desired phase should be stable over the broadest possible temperature range.
The individual pixels of an LC display are usually arranged in an x,y matrix formed by the arrangement of a series of electrodes (conductor tracks) along the rows and a series of electrodes along the columns on the upper or lower side of the display. The points of intersection of the horizontal (row) electrodes and the vertical (column) electrodes form addressable pixels.
This arrangement of the pixels is usually referred to as a passive matrix. For addressing, various multiplex schemes have been developed, as described, for example, in Displays 1993, Vol. 14, No. 2, pp. 86-93, and Kontakte 1993 (2), pp. 3-14. Passive matrix addressing has the advantage of simpler display production and consequently lower production costs, but the disadvantage that passive addressing can only be carried out line by line, which results in the addressing time for the entire screen with N lines being N times the line addressing time. For usual line addressing times of about 50 microseconds, this means a screen addressing time of about 60 milliseconds in, for example, the HDTV (high definition TV, 1152 lines) standard, i.e. a maximum frame rate of about 16 Hz, too slow for displaying moving images. In addition, display of gray shades is difficult. At the FLC Conference in Brest, France (Jul. 20-24, 1997, see Abstract Book 6th International Conference on Ferroelectric Liquid Crystals, Brest/France), a passive FLC display with digital gray shades was shown by Mizutani et al., in which each of the RGB pixels (RGB=red, green, blue) was divided into sub-pixels, allowing the display of gray shades in digital form through partial switching. Using three basic colors (red, green, blue), N gray shades result in 3N colors. The disadvantage of this method is the considerable increase in the number of screen drivers necessary and thus in the costs.
In the case of the display shown in Brest, three times as many drivers were necessary as in a standard FLC display without digital gray shades.
In so-called active matrix technology (AMLCD), a nonstructured substrate is usually combined with an active matrix substrate. An electrically non-linear element, for example a thin-film transistor, is integrated into each pixel of the active matrix substrate. The nonlinear elements can also be diodes, metal-insulator-metal and similar elements, which are advantageously produced by thin-film processes and are described in the relevant literature; see, for example, T. Tsukuda, TFT/LCD: Liquid Crystal Displays Addressed by Thin-Film Transistors, Gordon and Breach, 1996, ISBN 2-919875-01-9, and the references cited therein.
Active matrix LCDs are usually operated with nematic liquid crystals in TN (twisted nematics), ECB (electrically controlled birefringence), VA (vertically aligned) or IPS (in-plane switching) mode. In each case, the active matrix generates an electric field of individual strength on each pixel, producing a change in alignment and thus a change in birefringence, which is in turn visible in polarized light. A severe disadvantage of these processes is the poor video capability owing to excessively slow response times of nematic liquid crystals.
For this and other reasons, liquid crystal displays based on a combination of ferroelectric liquid crystal materials and active matrix elements have been proposed, see for example WO 97/12355, or Ferroelectrics 1996, 179,141-152, W. J. A. M. Hartmann, IEEE Trans. Electron. Devices 1989, 36 (9; Pt. 1), 1895-9, and dissertation, Eindhoven, The Netherlands, 1990.
Hartmann utilized a combination of the so-called xe2x80x9cquasi-bookshelf geometryxe2x80x9d (QBG) of an FLC and a TFT (thin-film transistor) active matrix to simultaneously achieve high response speed, gray shades and high transmission. However, the QBG is not stable over a broad temperature range, since the temperature dependence of the smectic layer thickness disrupts or rotates the field-induced layer structure. Moreover, Hartmann utilizes an FLC material having a spontaneous polarization of more than 20 nC/cm2, which, for pixels having realistic dimensions of, for example, an area of 0.01 mm2, leads to high electric charges (at saturation, Q=2 A P, A=pixel area, P=spontaneous polarization). With low-cost amorphous silicium TFTs, for example, these high charges cannot reach the pixel in the course of the opening time of the TFT. For these reasons, this technology has not been pursued any further to date. While Hartmann utilizes the charge-controlled bistability to display a virtually continuous gray scale, Nito et al. have suggested a monostable FLC geometry (see Journal of the SID, xc2xd, 1993, pages 163-169) in which the FLC material is aligned by means of relatively high voltages such that only a single stable position results from which a number of intermediate states are generated by application of an electric field via a thin-film transistor. These intermediate states correspond to a number of different brightness values (gray shades) when the cell geometry is matched between crossed polarizers.
One disadvantage of this technique, however, is the occurrence of a streaky texture in the display which limits contrast and brightness of this cell (see FIG. 8 in the abovementioned citation). While it is possible to correct the disadvantageous streaky texture by treatment with a high electric voltage (20-50 V) in the nematic or cholesteric phase (see page 168 of the abovementioned citation), such a field treatment is unsuitable for mass production of screens and usually does not result in temperature-stable textures either. Furthermore, this method produces switching only in an angle range of up to a maximum of once the tilt angle, which is about 22xc2x0 in the case of the material used by Nito et al. (cf. p. 165, FIG. 6) and thus produces a maximum transmission of only 50% of the transmission of two parallel polarizers.
The object of the present invention is to provide a ferroelectric active matrix liquid crystal display comprising a ferroelectric liquid-crystal mixture, where the liquid-crystal mixture assumes a monostable position, but without forming a streaky texture, is light- and temperature-stable and makes it possible to achieve a very high maximum transmission and a very high contrast.
Not Applicable.
This object is achieved according to the invention by a monostable ferroelectric active matrix display comprising a liquid-crystal layer in the form of a monodomain having an unambiguously defined direction of the layer normal z of the smC* phase, wherein the layer normal z and the preferential direction n of the nematic or cholesteric phase (N* phase) form an angle of more than 5xc2x0, where the liquid-crystal layer is composed of a liquid-crystal mixture of at least 5 compounds, which consists of an achiral base mixture comprising at least one compound from the group (I) consisting of (Ia-Ik), and, if desired, additionally at least one compound from the group consisting of (IIa-IIg) and/or at least one compound from group (III), and at least one chiral component from group (IV)
(Ia) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below
(Ib) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below
(Ic) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below
(Id) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3(M4A4)c(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below
(Ie) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below
(If) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below
(Ig) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below
(Ih) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below (Ii) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below:
R1 and R2 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R1 and R2 cannot both be hydrogen
A1, A2, A4 and A5 are, independently of one another, identical or different and are each 1,4-phenylene, unsubstituted, monosubstituted or disubstituted by F or Cl, cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 1-alkyl-1-sila-cyclohexane-1,4-diyl, bicyclo-[2.2.2]octane-1,4-diyl, indane-2,6-diyl, naphthalene-2,6-diyl
M1, M2, M4 and M5 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, (Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x95x90Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero
(Ik) R1(xe2x80x94A1xe2x80x94M1)a(xe2x80x94A2xe2x80x94M2)bxe2x80x94A3xe2x80x94(M4xe2x80x94A4)cxe2x80x94(M5xe2x80x94A5)dxe2x80x94R2 
xe2x80x83where A3 is 
xe2x80x83and the remaining substituents are as defined below:
R1 and R2 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R1 and R2 cannot both be hydrogen
G1xe2x80x94G2 is xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94CH2CH2xe2x80x94
n is zero or one
A1, A2, A4 and A5 are, independently of one another, identical or different and are each 1,4-phenylene, unsubstituted, monosubstituted or disubstituted by F or Cl, or cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F,
M1, M2, M4 and M6 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, (Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 0xe2x89xa6{a+b+c+d}xe2x89xa62 and the understanding that Mx is a single bond when the corresponding index is zero,
(IIa) R3(xe2x80x94A7xe2x80x94M7)a(xe2x80x94A8xe2x80x94M8)bxe2x80x94A6xe2x80x94(M9xe2x80x94A9)axe2x80x94(M10xe2x80x94A10)dxe2x80x94R4 
xe2x80x83where A6 is 
R3 and R4 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R3 and R4 cannot both be hydrogen
A7, A8, A9 and A10 are, independently of one another, identical or different and are each 1,4-phenylene, cyclohexane-1,4-diyl, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl or bicyclo-[2.2.2]octane-1,4-diyl,
M7, M8, M9 and M10 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(IIb) R3(xe2x80x94A7xe2x80x94M7)a(xe2x80x94A8xe2x80x94M8)bxe2x80x94A6xe2x80x94(M9xe2x80x94A9)c(M10xe2x80x94A10)dxe2x80x94R4 
xe2x80x83where A6 is 
R3 and R4 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R3 and R4 cannot both be hydrogen
A7, A8, A9 and A10 are, independently of one another, identical or different and are each 1,4-phenylene, unsubstituted or monosubstituted or disubstituted by F or Cl, cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 1-alkyl-1-sila-cyclohexane-1,4-diyl, bicyclo-[2.2.2]octane-1,4-diyl, indane-2,6-diyl, naphthalene-2,6-diyl
M7, M8, M9 and M10 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(IIc) R3(xe2x80x94A7xe2x80x94M7)a(xe2x80x94A8xe2x80x94M8)bxe2x80x94A6xe2x80x94(M9xe2x80x94A9)cxe2x80x94(M10xe2x80x94A10)dxe2x80x94R4 
xe2x80x83where A6 is 
R3 and R4 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl with the proviso that R3 and R4 cannot both be hydrogen
M7, M8, M9 and M10 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
A7, A8, A9 and A10 are, independently of one another, identical or different and are each 1,4-phenylene, unsubstituted or monosubstituted or disubstituted by F or Cl, cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 1-alkyl-1-sila-cyclohexane-1,4-diyl, bicyclo-[2.2.2]octane-1,4-diyl, indane-2,6-diyl,
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(IId) R3(xe2x80x94A7xe2x80x94M7)a(xe2x80x94A8xe2x80x94M8)bxe2x80x94A6xe2x80x94(M9xe2x80x94A9)cxe2x80x94(M10xe2x80x94A10)dxe2x80x94R4 
xe2x80x83where A6 is 
R3 and R4 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R3 and R4 cannot both be hydrogen
A7, A8, A9 and A10 are, independently of one another, identical or different and are each 1,4-phenylene, cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 1-alkyl-1-sila-cyclohexane-1,4-diyl, bicyclo-[2.2.2]octane-1,4-diyl, naphthalene-2,6-diyl,
M7, M8, M9 and M10 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(IIe) R3(xe2x80x94A7xe2x80x94M7)a(xe2x80x94A8xe2x80x94M8)bxe2x80x94A6xe2x80x94(M9xe2x80x94A9)cxe2x80x94(M10xe2x80x94A10)dxe2x80x94R4 
xe2x80x83where A6 is 
R3 and R4 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced, by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R3 and R4 cannot both be hydrogen
A7, A8, A9 and A10 are, independently of one another, identical or different and are each cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl,
M7, M8, M9 and M10 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(IIf) R3(xe2x80x94A7xe2x80x94M7)a(xe2x80x94A8xe2x80x94M8)bxe2x80x94A6xe2x80x94(M9xe2x80x94A9)cxe2x80x94(M10xe2x80x94A10)dxe2x80x94R4 
xe2x80x83where A6 is 
R3 and R4 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R3 and R4 cannot both be hydrogen
A7, A8, A9 and A10 are, independently of one another, identical or different and are each 1,4-phenylene, cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl
M7, M8, M9 and M10 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(IIg) R3(xe2x80x94A7M7)a(xe2x80x94A8xe2x80x94M8)bxe2x80x94A6xe2x80x94(M9xe2x80x94A9)cxe2x80x94(M10xe2x80x94A10)dxe2x80x94R4 
xe2x80x83where A6 is 
R3 and R4 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R1 and R2 cannot both be hydrogen
A7, A8, A9 and A10 are, independently of one another, identical or different and are each cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl,
M7, M8, M9 and M10 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(IIh) R3(xe2x80x94A7xe2x80x94M7)axe2x80x94A8xe2x80x94M8)bxe2x80x94A6xe2x80x94(M9xe2x80x94A9)cxe2x80x94(M10xe2x80x94A10)dxe2x80x94R4 
xe2x80x83where A6 is 
R3 and R4 are, independently of one another, identical or different and are each hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F with the proviso that R3 and R4 cannot both be hydrogen
A7, A8, A9 and A10 are, independently of one another, identical or different and are each cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl,
M7, M8, M9 and M10 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(III) R5(xe2x80x94A11xe2x80x94M11)a(xe2x80x94A12M-12)bxe2x80x94A13 
xe2x80x83where A13 is 
xe2x80x83and
X1, X2 and X3 are, independently of one another, identical or different and are each H, Cl, F, OCF2H or CF3 with the proviso that at least one of X1, X2 and X3 is not H,
R5 is hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F
A11 and A12 are, independently of one another, identical or different and are each 1,4-phenylene, cyclohexane-1,4-diyl, cyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 1-alkyl-1-sila-cyclohexane-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl, indane-2,6-diyl, naphthalene-2,6-diyl,
M11 and M12 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
a, b, d and c, are each zero or 1 with the proviso that 1xe2x89xa6{a+b}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero,
(IV) R6(xe2x80x94A14xe2x80x94M14)a(xe2x80x94A15xe2x80x94M15)bxe2x80x94(M16xe2x80x94A16)c(M17xe2x80x94A17)dxe2x80x94M18xe2x80x94R7 
xe2x80x83where
R6 is hydrogen, alkyl or alkyloxy having 2-12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may be replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94Si(CH3)2xe2x80x94 or cyclopropane-1,2-diyl and one or more H atoms may also be replaced by F
R7 is a moiety having at least one asymmetric carbon atom which is either part of an alkyl group having 3 to 12 carbon atoms, where one or two xe2x80x94CH2xe2x80x94 groups may also be replaced by xe2x80x94Oxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94 or xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94 and one of the substituents of the asymmetric carbon atom must be xe2x80x94CH3, xe2x80x94CF3, xe2x80x94OCH3, xe2x80x94CH3, Cl or F, or part of a 3- to 7-membered carbocycle, where one or two nonadjacent xe2x80x94CH2xe2x80x94 groups may also be replaced by xe2x80x94Oxe2x80x94 or onexe2x80x94CH2xe2x80x94 group may be replaced by xe2x80x94OC(xe2x95x90O)xe2x80x94 or xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94,
A14, A15, A16 and A17 are, independently of one another, identical or different and are each 1,4-phenylene, unsubstituted, monosubstituted or disubstituted by F or Cl, 1,3-phenylene, unsubstituted, monosubstituted or disubstituted by F or Cl, cyclohexane-1,4-diyl, unsubstituted or monosubstituted by F or CN, cyclohex-1-ene-1,4-diyl, 1-fluorocyclohex-1-ene-1,4-diyl, cyclohex-2-ene-1,4-diyl, 2-oxocyclohexane-1,4-diyl, 2-cyclohexen-1-one-3,6-diyl, 1-alkyl-1-sila-cyclohexane-1,4-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[4.5]decane-2,8-diyl, spiro[5.5]undecane-3,9-diyl, indane-2,6-diyl, naphthalene-2,6-diyl, unsubstituted, monosubstituted or disubstituted by F or CN, pyrimidine-2,5-diyl, pyridine-2,5-diyl, pyrazine-2,5-diyl, pyridazine-3,6-diyl, quinoline-2,6-diyl, quinoline-3,7-diyl, isoquinoline-3,7-diyl, quinazoline-2,6-diyl, quinoxaline-2,6-diyl, 1,3-dioxane-2,5-diyl, thiophene-2,4-diyl, thiophene-2,5-diyl, 1,3-thiazole-2,4-diyl, 1,3-thiazole-2,5-diyl, benzthiazole-2,6-diyl, 1,3,4-thiadiazole-2,5-diyl, piperidine-1,4-diyl or piperazine-1,4-diyl,
M14, M15, M16 and M17 are, independently of one another, identical or different and are each a single bond, xe2x80x94OC(xe2x95x90O)xe2x80x94, xe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94CH2CH2xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94
M18 is a single bond, if the moiety having the asymmetric carbon atom is part of an alkyl chain, and a single bond, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94OC(xe2x95x90O)xe2x80x94 or C(Oxe2x95x90)Oxe2x80x94, if the asymmetric carbon atom is part of the carbocycle defined under R7 
a, b, c and d are each zero or 1 with the proviso that 1xe2x89xa6{a+b+c+d}xe2x89xa63 and the understanding that Mx is a single bond when the corresponding index is zero.
Preferred mixtures have one or more of the following features:
R1 and R2 or R3 and R4, respectively, are each straight-chain alkyl or alkoxy having 2 to 12 carbon atoms the mixture comprises at least one compound in which, in R1 or R2 or R3 or R4, one nonterminal xe2x80x94CH2xe2x80x94 group is replaced by xe2x80x94OC(xe2x95x90O)xe2x80x94
in at least one compound of the formulae (I) or (II), in R1 and/or R2 and/or R3 or R4, at least one or more xe2x80x94CH2xe2x80x94 groups, but not the xe2x80x94CH2xe2x80x94 group adjacent to the nucleus, is replaced by xe2x80x94CF2xe2x80x94
in at least one compound of the formulae (I) or (II), R1 or R2 or R3 or R4 is hydrogen
R7 is sec-alkyl or sec-alkoxy having 4 to 12 carbon atoms
R7 is 2-methylalkyl or 2-methylalkoxy or 2-methylalkylcarbonyloxy or 2-methylalkyloxycarbonyl having 4 to 12 carbon atoms
R7 is 2-fluoroalkyl or 2-fluoroalkoxy or 2-fluoroakylcarbonyloxy or 2-fluoroalkyloxycarbonyl having 3 to 12 carbon atoms
R7 is 2-trifluoromethylalkyl or 2-trifluoromethylalkoxy or 2-trifluoromethylalkylcarbonyloxy or 2-trifluoromethylalkyloxycarbonyl having 3 to 12 carbon atoms
R7 comprises the group [xe2x80x94Oxe2x80x94CH(CH3)xe2x80x94C(xe2x95x90O)Oxe2x80x94] as part of an alkyl chain,
R7 comprises the group xe2x80x94C(xe2x95x90O)Oxe2x80x94 as part of a 5- or 6-membered cycle
R7 comprises the group oxirane-2,3-diyl.
The achiral base mixture may additionally comprise at least one compound having a phenylpyrimidine, fluorophenylpyrimidine, difluorophenyl-pyrimidine, phenylpyridine, fluorophenylpyridine or difluorophenylpyridine group. In this case, the presence of 3 or more of these compounds is preferred. Preference is given to achiral compounds having (difluoro)phenylpyrimidine groups. The mixture may additionally comprise compounds having benzthiazole-2,6-diyl or thiophene-2,5-diyl groups.
The achiral base mixture may comprise at least one compound having one fluorine atom, at least one compound having two fluorine atoms, and at least one of these compounds may additionally comprise a heterocyclic group, if desired.
The achiral base mixture may preferably comprise at least one compound of the formula (Ia), at least one compound of the formula (Ib) and preferably at least one compound of the formula (Ig). These compounds may additionally contain one of the abovementioned heterocyclic groups.
The proportion of heterocycles in the liquid-crystal mixture can be more than 20% by weight, preferably more than 30% by weight, particularly preferably more than 40% by weight, based on the total liquid-crystal mixture. These are preferably at least two phenylpyrimidines or difluorophenylpyrimidines and at least one compound having a benzthiazole-2,6-diyl group and at least one compound having a thiophene-2,5-diyl group.
The base mixture may comprise at least one, preferably at least two, particularly preferably at least three, difluoroterphenyl compounds.
In the chiral compounds of the formula (IV), the chiral center may preferably be located in a fluoroalkyl, (trifluoromethyl)alkyl, methylalkyl or oxirane group.
The active matrix FLCD of the invention comprises, as optically active layer, a ferroelectric liquid-crystalline medium (liquid-crystal phase) having a phase sequence of
isotropicxe2x80x94nematic or cholesteric (N*)xe2x80x94smectic C*
or a phase sequence of
isotropicxe2x80x94nematic or cholesteric (N*)xe2x80x94smectic A*xe2x80x94smectic C*,
where the smectic A* phase has a range of existence (phase range) of not more than 2xc2x0 C., preferably not more than 1xc2x0 C., particularly preferably not more than 0.5xc2x0 C. The asterisk (*) attached to the phase name indicates a chiral phase.
The FLC mixtures exhibit high resistance and voltage retaining ability values.
The displays are preferably produced by a process which comprises introducing the liquid-crystal layer into the space between a rubbed upper substrate plate and a rubbed lower substrate plate of the active matrix display, the rubbing directions on the upper substrate plate and the lower substrate plate being essentially parallel, and cooling the liquid-crystal phase from the isotropic phase, a direct electric current being applied to the display at least during the N*xe2x86x92smC* or N*xe2x86x92smA*xe2x86x92smC* phase transition.
The FLC mixture is filled into an active matrix display. Production and components of an AM display of this type are described in detail in the above-cited Tsukuda reference. However, in contrast to nematic displays, the thickness of the FLC layer is only from 0.7 to 2.5 xcexcm, preferably 1-2 xcexcm. Moreover, the rubbing directions on upper and lower substrate plates are essentially parallel. The term xe2x80x9cessentially parallelxe2x80x9d includes antiparallel rubbing directions or rubbing directions which are weakly crossed, i.e. up to 10xc2x0.
It is important for the operation of this display that in the production of the display, during controlled cooling, a direct electric current, preferably of less than 5 V, is applied and maintained during the N*xe2x86x92smC* or Nxe2x86x92smA*xe2x86x92smC* phase transition, with the result that the whole display assumes a monostable monodomain which appears completely dark between crossed polarizers.
Once this domain has been obtained, the direct current is switched off. In contrast to the abovementioned approach by Hartmann or conventional bistable FLCDs, the resulting texture is monostable. This means that the preferred n director (which indicates the preferential direction of the long axes of the molecules) is in the rubbing direction of the cell, whereas the z director (which indicates the preferential direction of the smectic layer normal) is oblique relative to the rubbing direction by approximately the tilt angle value. This configuration is exactly the opposite of the conventional bistable cell according to Clark and Lagerwall in which the z director is in the rubbing direction.
In contrast to Nito""s approach, this is exactly the orientation in which there are no two layer normals, and thus no two orientation domains, which ultimately lead to the unwanted streaky texture described above, but a single unambiguous direction of the z director and thus a single monodomain only. Furthermore, it is possible to obtain twice the tilt angle, which leads to 100% transmission, based on parallel polarizers, i.e. double brightness is achieved.
The display thus obtained appears completely dark at a suitable angle of rotation between crossed polarizers. On applying an addressing voltage of only a few volts, the display appears bright, it being possible to vary the brightness continuously by means of the voltage, and is almost as bright as two parallel polarizing films when saturated. An important feature of this display is that the angle between the preferential direction of the nematic (or cholesteric) phase and the layer normal (z director) is ideally equal to the tilt angle of the smectic C phase, or at least essentially equal to the tilt angle. For the purposes of the invention, xe2x80x9cessentiallyxe2x80x9d means preferably a range from half the tilt angle to the full tilt angle, particularly preferably from 0.8 to 1.0 times the tilt angle, but at least 5xc2x0.
The ferroelectric active matrix liquid crystal display of the invention is very useful in practice, in particular for TV, HDTV or multimedia, since it combines high transmission, short response times, gray scale and thus full color capability, low-cost production and a broad temperature range. Furthermore, the display can be operated at voltages of 10 volts, preferably of xe2x89xa68 V, particularly preferably of xe2x89xa65 V.
In particular, the term xe2x80x9cactive matrix displayxe2x80x9d as used herein includes an LCD in which one of the two substrates is replaced by the rear side of an IC chip (IC=integrated circuit) as described, for example, in D. M. Walba, Science 270, 250-251 (1993) or http://www.displaytech.com.
The spontaneous polarization of the active matrix FLCD of the invention is preferably less than 15 nC/cm2, preferably in the range of from 0.01 to 10 nC/cm2 at the operating temperature of the display.
The length of the chiral nematic or cholesteric pitch in the liquid-crystal layer is preferably more than 50 xcexcm in a temperature range of at least 2xc2x0 C. above the smectic phase transition.
The displays may be used for example in the TV, HDTV or multimedia areas or in the area of information processing, e.g. in notebook PCs, personal digital assistants or desktop monitors.
The processes for producing the materials which are suitable for the mixtures of the invention are known in principle, as is the production of liquid-crystal mixtures from the individual components. For example, compounds of the respective formulae below are described in:
(Ia) EP-B-0 210215 and GB-B 2198743
(Ib) EP-B-0 210 215 and JP-B 2732765
(Ic) Gray et al., Mol. Cryst.Liq. Cryst. 1991, vol. 204, pp. 43-64
(Id) Gray et al., Mol. Cryst.Liq. Cryst. 1991, vol. 204, pp. 43-64
(Ie) EP-B 602596
(If) Xu et al., Liq. Cryst. 1995, 18(1), 105-8
(Ig) JP-A 09052859
(Ih) DE-A 19522167
(Ii) DE-A-196 52252
(Ik) U.S. Pat. No. 5,648,021
(IIa) Flxc3xcssige Kristalle in Tabellen II [Liquid Crystals in Tables II], pp. 269-304
(IIb) U.S. Pat. No. 5,447,656
(IIc) Flxc3xcssige Kristalle in Tabellen II [Liquid Crystals in Tables II], pp. 313-322
(IId) EP-A-0 546 338
(IIe) Flxc3xcssige Kristalle in Tabellen II [Liquid Crystals in Tables II], pp. 32-72
(IIf) EP-A-0 761 674, 742 222, 732 335, 727 428 etc.
(IIg) Flxc3xcssige Kristalle in Tabellen II [Liquid Crystals in Tables II], pp. 85-95
(III) EP-A-0 832 954
(IV) chiral dopants having, as moiety comprising an asymmetric
carbon atom,
oxirane EP-B-0 292 954/263 437
dioxolane EP-B-0 351 746/361 272
2,3-difluoroalkyloxy U.S. Pat. No. 5,501,506
2-fluoroalkyloxy U.S. Pat. No. 4,798,680
xcex1-chlorocarboxylate U.S. Pat. No. 4,855,429
xcex1-fluorocarboxylate Arakawa et al., Liquid Crystals 1997, vol. 23, no. 5 p. 659-666
methyl-branched alkyl chains EP-B-0 201 578, 211 030
lactones e.g. U.S. Pat. Nos. 5,061,398, 5,256,330, 5,026,506
and compounds containing the structural elements
silylalkyl from EP-B0 366561
cyclopropylalkyl from EP-B-0 318423/398155
perfluoroalkyl from Ferroelectrics 1988, 85, 375-384, or U.S. Pat. Nos. 4,886,619, 5,082,587, 5,254,747, 5,262,082, 5,437,812 or 5,482,650
perfluorocylohexyl from DE-A-197 48818